During adolescence, relationships with friends become the primary environment where social interaction and development occurs. This has both positive and negative consequences. On the positive side, the peer group provides companionship, social and emotional support, as well as opportunities for self-reflection which parents are, at times, unable to offer (Oppenheimer & Hankin 2011:486-493; Chen, Cohen, Johnson & Kasen 2009:223). However, interaction with peers may also have negative effects. Interaction with peers may be associated with undesirable behaviour such as alcohol or drug abuse (Henry, Slater & Oetting 2005:275-283; Allen, Donohue, Griffin, Ryan & Turner 2003:163-186). Also, peers may socially isolate a particular individual and this can have negative consequences for the person's social development, emotional functioning and self-image resulting in depression (Oppenheimer & Hankin 2011:487). Furthermore, adolescents who are socially victimised find it difficult to establish normal social relationships with friends and these adolescents are likely to succumb to group pressure simply to be accepted. Relationship with parents, relationship with friends and self-image are some of the most prominent factors relating to group pressure (Bámaca & Umaha-Taylor 2006:633-634; La Greca & Harrison 2005:58; Fourie 2001:210-213; Kung & Farrell 2000:509). These factors are all psychosocial in nature and do not precisely explain how adolescents cognitively think and reason about social issues in their lives and how this might affect their vulnerability to group pressure. Adolescents should be able to think abstractly and reason in a logical way (Woolfolk 2010:38-39) but, even if they can, this is no guarantee that they will be capable of rational reasoning. Adolescents, like many adults, often reason in an irrational way and come to conclusions without supporting evidence. Adolescents who think irrationally tend to make incorrect assumptions about themselves, other people and about situations in general. These faulty and often illogical deductions result in beliefs which in turn, lead to destructive emotions and deviant behaviour. Ellis (in Maltby, Day & Macaskill 2007:458-459) identified a number of irrational beliefs which he considers to be the root of many emotional and behavioural problems. The aims of the current research revolve around the relationship between these irrational beliefs and group pressure. A sample of 316 high school learners (120 boys and 196 girls) from various provinces in South Africa was used in the investigation. The average age of the respondents was 16.03 years with a standard deviation of 1.29. Irrational beliefs were measured using a questionnaire developed by Jones (1968). The questionnaire measures the ten most common irrational beliefs identified by Ellis (Maltby, Day & Macaskill 2007:458-459). Other variables namely group pressure, relationship with peers, parent-child relationship and self-image were measured using a questionnaire developed by Fourie (2001). Seven of the ten irrational beliefs correlated positively with group pressure which indicates that the phenomenon of strongly held irrational beliefs is related to intense group pressure among adolescents. From the results of a regression analysis, three irrational beliefs were identified as the most prominent beliefs as far as group pressure is concerned. These irrational beliefs are: that other people should always like and accept you, that problems should be avoided rather than solved and that you cannot manage in life without somebody else's help.